The present invention relates to machine-readable displays, that is to say display primarily intended to be read by machine although the displays may also be capable of being read by humans. More specifically, this invention relates to machine-readable displays which can display a bar code or similar machine-readable image based upon stored information or external inputs. The present displays may be useful in various information display applications, and in particular for the display of information concerning goods in a retail or similar environment. The present invention is especially, though not exclusively, intended for use in displays containing encapsulated electrophoretic media.
In the displays of the present invention, the electro-optic medium will typically be a solid (such displays may hereinafter for convenience be referred to as “solid electro-optic displays”), in the sense that the electro-optic medium has solid external surfaces, although the medium may, and often does, have internal liquid- or gas-filled spaces. Thus, the term “solid electro-optic displays” includes encapsulated electrophoretic displays, encapsulated liquid crystal displays, and other types of displays discussed below.
The term “electro-optic”, as applied to a material or a display, is used herein in its conventional meaning in the imaging art to refer to a material having first and second display states differing in at least one optical property, the material being changed from its first to its second display state by application of an electric field to the material. Although the optical property is typically color perceptible to the human eye, it may be another optical property, such as optical transmission, reflectance, luminescence or, in the case of displays intended for machine reading, pseudo-color in the sense of a change in reflectance of electromagnetic wavelengths outside the visible range.
The terms “bistable” and “bistability” are used herein in their conventional meaning in the art to refer to displays comprising display elements having first and second display states differing in at least one optical property, and such that after any given element has been driven, by means of an addressing pulse of finite duration, to assume either its first or second display state, after the addressing pulse has terminated, that state will persist for at least several times, for example at least four times, the minimum duration of the addressing pulse required to change the state of the display element. It is shown in published U.S. Patent Application No. 2002/0180687 that some particle-based electrophoretic displays capable of gray scale are stable not only in their extreme black and white states but also in their intermediate gray states, and the same is true of some other types of electro-optic displays. This type of display is properly called “multi-stable” rather than bistable, although for convenience the term “bistable” may be used herein to cover both bistable and multi-stable displays.
Several types of electro-optic displays are known. One type of electro-optic display is a rotating bichromal member type as described, for example, in U.S. Pat. Nos. 5,808,783; 5,777,782; 5,760,761; 6,054,0716,055,091; 6,097,531; 6,128,124; 6,137,467; and 6,147,791 (although this type of display is often referred to as a “rotating bichromal ball” display, the term “rotating bichromal member” is preferred as more accurate since in some of the patents mentioned above the rotating members are not spherical). Such a display uses a large number of small bodies (typically spherical or cylindrical) which have two or more sections with differing optical characteristics, and an internal dipole. These bodies are suspended within liquid-filled vacuoles within a matrix, the vacuoles being filled with liquid so that the bodies are free to rotate. The appearance of the display is changed to applying an electric field thereto, thus rotating the bodies to various positions and varying which of the sections of the bodies is seen through a viewing surface. This type of electro-optic medium is typically bistable.
Another type of electro-optic display uses an electrochromic medium, for example an electrochromic medium in the form of a nanochromic film comprising an electrode formed at least in part from a semi-conducting metal oxide and a plurality of dye molecules capable of reversible color change attached to the electrode; see, for example O'Regan, B., et al., Nature 1991, 353, 737; and Wood, D., Information Display, 18(3), 24 (March 2002). See also Bach, U., et al., Adv. Mater., 2002, 14(11), 845. Nanochromic films of this type are also described, for example, in U.S. Pat. No. 6,301,038, International Application Publication No. WO 01/27690, and in U.S. patent application 2003/0214695. This type of medium is also typically bistable.
Another type of electro-optic display, which has been the subject of intense research and development for a number of years, is the particle-based electrophoretic display, in which a plurality of charged particles move through a suspending fluid under the influence of an electric field. Electrophoretic displays can have attributes of good brightness and contrast, wide viewing angles, state bistability, and low power consumption when compared with liquid crystal displays. Nevertheless, problems with the long-term image quality of these displays have prevented their widespread usage. For example, particles that make up electrophoretic displays tend to settle, resulting in inadequate service-life for these displays.
As noted above, electrophoretic media require the presence of a suspending fluid. In most prior art electrophoretic media, this suspending fluid is a liquid, but electrophoretic media can be produced using gaseous suspending fluids; see, for example, Kitamura, T., et al., “Electrical toner movement for electronic paper-like display”, TDW Japan, 2001, Paper HCS1-1 and Yamaguchi, Y, et al., “Toner display using insulative particles charged triboelectrically”, IDW Japan, 2001, Paper AMD4-4). See also European Patent Applications 1,429,178; 1,462,847; and 1,482,354; and International Applications WO 2004/090626; WO 2004/079442; WO 2004/077140; WO 2004/059379; WO 2004/055586; WO 2004/008239; WO 2004/006006; WO 2004/001498; WO 03/091799; and WO 03/088495. Such gas-based electrophoretic media appear to be susceptible to the same types of problems due to particle settling as liquid-based electrophoretic media, when the media are used in an orientation which permits such settling, for example in a sign where the medium is disposed in a vertical plane. Indeed, particle settling appears to be a more serious problem in gas-based electrophoretic media than in liquid-based ones, since the lower viscosity of gaseous suspending fluids as compared with liquid ones allows more rapid settling of the electrophoretic particles.
Numerous patents and applications assigned to or in the names of the Massachusetts Institute of Technology (MIT) and E Ink Corporation have recently been published describing encapsulated electrophoretic media. Such encapsulated media comprise numerous small capsules, each of which itself comprises an internal phase containing electrophoretically-mobile particles suspended in a liquid suspending medium, and a capsule wall surrounding the internal phase. Typically, the capsules are themselves held within a polymeric binder to form a coherent layer positioned between two electrodes. Encapsulated media of this type are described, for example, in U.S. Pat. Nos. 5,930,026; 5,961,804; 6,017,584; 6,067,185; 6,118,426; 6,120,588; 6,120,839; 6,124,851; 6,130,773; 6,130,774; 6,172,798; 6,177,921; 6,232,950; 6,249,271; 6,252,564; 6,262,706; 6,262,833; 6,300,932; 6,312,304; 6,312,971; 6,323,989; 6,327,072; 6,376,828; 6,377,387; 6,392,785; 6,392,786; 6,413,790; 6,422,687; 6,445,374; 6,445,489; 6,459,418; 6,473,072; 6,480,182; 6,498,114; 6,504,524; 6,506,438; 6,512,354; 6,515,649; 6,518,949; 6,521,489; 6,531,997; 6,535,197; 6,538,801; 6,545,291; 6,580,545; 6,639,578; 6,652,075; 6,657,772; 6,664,944; 6,680,725; 6,683,333; 6,704,133; 6,710,540; 6,721,083; 6,727,881; 6,738,050; 6,750,473; and 6,753,999; and U.S. Patent Applications Publication Nos. 2002/0019081; 2002/0021270; 2002/0060321; 2002/0063661; 2002/0090980; 2002/0113770; 2002/0130832; 2002/0131147; 2002/0171910; 2002/0180687; 2002/0180688; 2002/0185378; 2003/0011560; 2003/0020844; 2003/0025855; 2003/0038755; 2003/0053189; 2003/0102858; 2003/0132908; 2003/0137521; 2003/0137717; 2003/0151702; 2003/0214695; 2003/0214697; 2003/0222315; 2004/0008398; 2004/0012839; 2004/0014265; 2004/0027327; 2004/0075634; 2004/0094422; 2004/0105036; 2004/0112750; and 2004/0119681; and International Applications Publication Nos. WO 99/67678; WO 00/05704; WO 00/38000; WO 00/38001; WO 00/36560; WO 00/67110; WO 00/67327; WO 01/07961; WO 01/08241; WO 03/107,315; WO 2004/023195; and WO 2004/049045.
Many of the aforementioned patents and applications recognize that the walls surrounding the discrete microcapsules in an encapsulated electrophoretic medium could be replaced by a continuous phase, thus producing a so-called polymer-dispersed electrophoretic display, in which the electrophoretic medium comprises a plurality of discrete droplets of an electrophoretic fluid and a continuous phase of a polymeric material, and that the discrete droplets of electrophoretic fluid within such a polymer-dispersed electrophoretic display may be regarded as capsules or microcapsules even though no discrete capsule membrane is associated with each individual droplet; see for example, the aforementioned 2002/0131147. Accordingly, for purposes of the present application, such polymer-dispersed electrophoretic media are regarded as sub-species of encapsulated electrophoretic media.
A related type of electrophoretic display is a so-called “microcell electrophoretic display”. In a microcell electrophoretic display, the charged particles and the suspending fluid are not encapsulated within microcapsules but instead are retained within a plurality of cavities formed within a carrier medium, typically a polymeric film. See, for example, International Application Publication No. WO 02/01281, and published US Application No. 2002/0075556, both assigned to Sipix Imaging, Inc.
Although electrophoretic media are often opaque (since, for example, in many electrophoretic media, the particles substantially block transmission of visible light through the display) and operate in a reflective mode, many electrophoretic displays can be made to operate in a so-called “shutter mode” in which one display state is substantially opaque and one is light-transmissive. See, for example, the aforementioned U.S. Pat. Nos. 6,130,774 and 6,172,798, and U.S. Pat. Nos. 5,872,552; 6,144,361; 6,271,823; 6,225,971; and 6,184,856. Dielectrophoretic displays, which are similar to electrophoretic displays but rely upon variations in electric field strength, can operate in a similar mode; see U.S. Pat. No. 4,418,346.
An encapsulated or microcell electrophoretic display typically does not suffer from the clustering and settling failure mode of traditional electrophoretic devices and provides further advantages, such as the ability to print or coat the display on a wide variety of flexible and rigid substrates. (Use of the word “printing” is intended to include all forms of printing and coating, including, but without limitation: pre-metered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, curtain coating; roll coating such as knife over roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; silk screen printing processes; electrostatic printing processes; thermal printing processes; inkjet printing processes; and other similar techniques.) Thus, the resulting display can be flexible. Further, because the display medium can be printed (using a variety of methods), the display itself can be made inexpensively.
For many applications, the ability for two electronic devices to interchange information is very important. While there are many methods available, including both hardwired and wireless methods, for example infra-red ports, Bluetooth, IEEE 802.11, Ethernet, all these methods share three drawbacks; they are expensive to implement, they require fairly large amounts of power, and including capabilities for these methods in a device will increase its size and weight. This last drawback can be a major problem in small portable devices such as personal digital assistants (PDA's), shelf tags or inventory/shipping labels.
One possible solution to these problems is to use a device's display as the output device for humans and machine reading. There are precedents for this kind of dual-use display; for example, Timex (Registered Trade Mark) makes a watch which can receive data from a computer by reading with a built-in photodetector a series of flashing patterns displayed on a cathode ray tube. Also, printed bar codes on labels can be read using a laser or LED scanner. If a rewriteable display material could display bar codes readable by standard equipment, the equipment would work with both paper labels and electronic labels.
Not all display materials can be used in this application. As illustrated in FIG. 1 of the accompanying drawings, which is a schematic side elevation of a bar code reader reading a bar code, the display material must meet certain requirements. FIG. 1 shows a substrate 100 bearing bar code markings 102 (a one-dimensional bar code is illustrated, but obviously a two-dimensional bar code could be used if desired) being read by a bar code reading head 104. The head 104 emits a scanning beam 106 which is reflected from the bar code markings 102 and detected by a photodetector (not shown) in the head 104 to effect readings of these markings. Since the head 104 reads the bar code markings 102 by measuring the reflected light from their surfaces using a laser or LED, any display material used to provide markings 102 must be reflective. Furthermore, since as illustrated in FIG. 1, the beam 104 is reflected back to the head 104 over a wide range of incident angles, any display material used must have nearly Lambertian reflective qualities. Finally, the display must have sufficient brightness to give a strong return signal, and sufficient contrast to differentiate between black and white bars.
The present invention provides a display which can be used to provide bar code markings readable by a bar code scanner.
The display of the present invention may be useful in, inter alia, retail stores. Modern retailing is under rising pressure to increase both the speed and accuracy with which it displays product information and price. The almost universal use of bar codes to identify both product type and price has enabled retailers to update the price of products from a central location and have that price automatically register when the bar code is scanned at the point-of-sale (POS). However, the speed with which retailers can update product information and price at the actual location where a product is displayed has not kept pace. The delay in updating product information and pricing at the point-of-display (POD) can lead to a mismatch between the price a consumer has been lead to believe a product costs and the price registered at the POS. A consumer confronted with a different price at the POS is understandably annoyed, and adverse business or regulatory consequences may follow for the retailer.
The delay in updating product information and price at the POD most frequently arises from the need to manually update this information. Today, retail establishments typically display product information and price on labels in the form of adhesive tags, preprinted cards or plastic numbers. The label is usually affixed to the edge of the shelf or surface on which the product is located. These labels must necessarily be changed manually; a time consuming and labor intensive process subject to a variety of human errors. The cost and chance for error associated with such manual change is compounded by the rapid change of product information and price, as well as location, in the modern retail establishment. The increasing use of such dynamic pricing schemes such as yield management pricing can only increase the probability of POD and POS price mismatch.
A need therefore exists in the retail environment to replace a large majority of the manual activity in the change cycle of POD product information and price with an electronic method that is inexpensive and flexible enough to be economically viable.
Electronic shelf price label (ESPL) systems have been proposed for displaying at the POD continuously updateable prices. Electronic display units for an ESPL system have been developed which can be affixed to the edge of the shelf, and which optically indicate the price of the merchandise and perhaps additional information. The electronic display units are connected to a store computer which can easily update the price on the electronic display unit as well as at the POS. As a result, it can generally be guaranteed that the price at the POD is the same as the price which will be charged at the POS.
Several important technical problems have prevented the cost effective development of ESPL display systems. Invariably, these systems required a near continuous supply of power, either by line transmission, battery, capacitor, RF transmission, or other form of indirect power transmission. Many systems, to date, involve a hard-wired connection from the individual electronic display units to the power supply. The expense associated with installing and maintaining such hard-wire systems has hindered their economic viability. In addition, the goods on the shelves in most retail establishments are constantly being rearranged. Consequently any direct hard-wired system becomes an expensive impracticality. Wireless power transmission systems have been proposed where the electronic display units inductively receive the energy emitted by a transmitter to recharge an integrated or hardwired power source, e.g., a battery. Nevertheless, these systems also invariably require a near constant supply of power to maintain the display of the electronic display units.
To date, a major cost driver of ESPL systems has been the electronic display unit and associated communication electronics. In a traditional ESPL system, there is one wired emissive electronic display unit affixed to the shelf for each SKU. Due to the expense of a high-contrast, high-resolution emissive electronic display, only the price portion of the label is variable; the rest of the label, such as the bar code and SKU information, is printed and permanent. As a result, manual labor is required to move the electronic display units whenever the corresponding product is moved.
The benefits flowing from installation of a viable, workable ESPL system would be many. Prices could be displayed at the POD for each of the many products for sale, and the price, electronically displayed, could be made to match with high reliability the price registered when the product is scanned at the POS. Sales and “specials” could be posted, and later cleared, with a minimal labor cost as compared to the common manual method of updating POD information. Further, a viable, workable ESPL system that provides an electronic display with the mechanical compatibility of a printed display could truly satisfy the needs of the retail environment. Such a system, could almost instantaneously, and store wide, update each and every POD display unit, and quite possibly enable in-store marketing methods never before thought possible.